Conventionally, the read characteristic of a NAND flash memory which exemplifies a semiconductor memory device is mainly determined by charge of bit lines. In such a NAND flash memory, with advances in micropatterning of the manufacturing process, the decrease in memory cell current and the mutual interference between adjacent bit lines become conspicuous, so the read characteristic may degrade.
Also, a read operation is performed in verify at the time of a write or erase operation in or from the NAND flash memory as well, so the write or erase characteristic may similarly degrade.